Implementation of the Circular Economy Concept in Greenhouse Hydroponics for Ultimate Use of Water and Nutrients

Abstract

The circular economy in agriculture aims to reduce waste while also making best use of residues by using economically viable processes and procedures to increase their value. In this study a two-level cascade cultivation system was set up under greenhouse conditions. The research was focused on the identification of crop species as secondary crops and the development/iterative optimization of cultivation practices. For this purpose, different crop-combinations with a primary and different secondary crops were investigated using different system-layouts. Measurements were carried out during two cultivation periods. During the 1st Period a combination of cucumber (Cucumis sativus) as primary crop, with rosemary (Rosmarinus officinalis), basil (Ocimum basilicum), and peppermint (Mentha piperita) as secondary crops, was evaluated. In the 2nd Period the drainage of tomato (Solanum lycopersicum) plants was re-used to irrigate spearmint (Mentha spicata), dill (Anethum graveolens), celery (Apium graveolens) and parsley (Petroselinum crispum) plants. In both periods, different fertigation management strategies based on the drainage solution of the primary crop were employed. The use of the cascade hydroponic system improved both crop water and nutrient use efficiency. Notably, the NO3 disposal was about 40% less as compared to a monoculture. Average fresh water consumption of secondary crop plants irrigated with diluted drainage solution was reduced by 30% in comparison to plants irrigated with fresh water.

Basil as Secondary Crop in Cascade Hydroponics: Exploring Salinity Tolerance Limits in Terms of Growth, Amino Acid Profile, and Nutrient Composition

“…Similar growth restrictions were also recorded in the T5 plants in the first experiment (Figures 1 and 2). Elvanidi et al (2020) [5] reported similar reductions of basil grown in cascade hydroponics in which basil received only 40% of cucumber drainage complemented with typical irrigation water. The total amino acid content of basil that received the drainage solution from cucumber (hereinafter referred to as "treated plants") displayed a trend for higher values compared to the control only at the final harvest (Figure 6).…”

“…Similar growth restrictions were also recorded in the T5 plants in the first experiment (Figures 1 and 2). Elvanidi et al (2020) [5] reported similar reductions of basil grown in cascade hydroponics in which basil received only 40% of cucumber drainage complemented with typical irrigation water.…”

“…This entails risks regarding impaired plant function and performance, which negatively affect crop yield [3,4]. Additionally, in both open and closed soilless systems, the discharge of used nutrient solutions to the environment further deteriorates soil quality, causing severe environmental degradation and a waste of resources [5]. The ultimate result of such management practices is a reduced sustainability of soilless systems, although their implementation has considerable advantages in terms of crop productivity, space utilization, and nutrient-use efficiency [6,7].…”

“…The ultimate result of such management practices is a reduced sustainability of soilless systems, although their implementation has considerable advantages in terms of crop productivity, space utilization, and nutrient-use efficiency [6,7]. Toward mitigating the environmental impacts of the discharge of waste nutrient solutions, a new concept in closed systems has been recently proposed that includes a transformation of the classical system into a cascade system; i.e., the used nutrient solution drained from a primary crop is subsequently directed to a secondary crop, and its drainage solution to a tertiary crop [5,8]. This exhaustive re-use of the same nutrient solution confers great advantages in resource-use efficiency while minimizing waste, and thus enhances the sustainability of cascade cultivation systems.…”

“…This exhaustive re-use of the same nutrient solution confers great advantages in resource-use efficiency while minimizing waste, and thus enhances the sustainability of cascade cultivation systems. Apparently, the suitability of certain crops to be used as secondary and tertiary crops should be carefully considered in terms of salt tolerance; it becomes a crucial characteristic due to increased salinity of the drained nutrient solution [5,9].…”